1. Field of the Invention
This invention relates to a lenticular lens having improved light distribution. More particularly, this invention relates to a lenticular lens and its use with electric lamps, said lens having multi-sided lenticules (i) contained in a plurality of sections circumferentially arranged in a circle around the optical center of the lens, with the lenticules in each section oriented to reduce or avoid parallelism and (ii) arranged in a plurality of zones concentric around the optical center of the lens with the size and light spreading ability of the lenticules in each zone selected to provide a uniform light distribution over the desired light beam pattern.
2. Background of the Disclosure
Exterior and interior lights such as flood and spotlights include an electric light source mounted within a reflector which is covered with a lens to break up the light source image and redirect the reflected light to the desired beam pattern to illuminate a particular zone or area. Uniform illumination is desired, but rarely achieved. The filament or arc discharge light source is three-dimensional and not a point source. This produces a light source image which must be broken up and diffused or eliminated by the lens. The lens type most commonly used and cheapest to manufacture for this purpose is a lenticulated lens made of light-transmissive glass or plastic containing a plurality of lenticules on the inner light receiving surface. These lenticules generally have a spherical or curved light entrance surface and terminate in a slightly curved or relatively flat exit surface. The lenticules are typically distributed across the lens in the form of a close packed, uniform, array of parallel rows and are therefore all of the same shape and size. In the case where the lenticules all have a spherical light-receiving surface, they are arranged in a close packed, uniform, hexagonal array of parallel rows. In theory, the spherical surface of the lenticules should produce a center weighted light distribution in the beam pattern with the light falling off smoothly in intensity toward the edge of the pattern. In fact this does not happen with lenses having lenticules in a uniform hexagonal array due to the physical properties of the glass, the lens molding process, the greater angular light bending strength in the corners of each lenticule and optical distortion at the edges of the hexagonal lenticules and the optical interaction of the hexagonal lenticules with the light source image reflected forward by the reflector into the lenticules. The uniform, close-packed hexagonal array of the hexagonally-shaped lenticules results in the same sides of all the lenticules being parallel. Each hexagonal-shaped lenticule produces a light beam having a hexagonal shaped perimeter, with the sides of the hexagonal perimeter being aligned with the sides of the lenticule. Since the same sides of all the lenticules are parallel, the hexagonal-shaped perimeter of the light beam projected forward through the lens is a summation of the hexagonal perimeter of the beams projected through all the lenticules. The light intensity of the straight sides of the hexagonal-shaped perimeter of the light pattern is exascerbated when a longitudinal light source image projected forward of the reflector is parallel to the sides of the lenticules. This is called "parallelism" and produces a light beam pattern which produces a light beam having a hexagonal perimeter which users refer to as the "hex pattern" and regard as objectionable.
By way of example, a close-packed hexagonal array of parallel rows of lenticules having a curved or spherical light-receiving surface distributed across the light-receiving side of a lens results in six different directions radially extending from the optical center of the lens to the optical edge of the lens, wherein the same side of each hexagonal lenticule is radially aligned parallel to the long axis of the light source images projected through the lenticules. This reinforces the filament or arc light source image projected in the six directions and produces the hexagonal-shaped light perimeter at the outer edge of the projected beam pattern. In the case of a circular lens, the beam pattern will be circular with a visibly discernible, hexagonal-shaped perimeter of light (hex pattern) around the outer edge of the beam pattern.
Furthermore, a light beam pattern is produced which the human eye perceives as light weighted in the center and edge of the pattern, with a lower level of light intensity in-between the center and edge. This gives a visual impression of a bright center surrounded by an apparent lower intensity light ring with a bright appearing light band or ring near the edge of the beam pattern. This ring of brighter or greater light intensity towards the edge is known as "the donut". Attempts to improve light distribution over the beam pattern have included a lenticular lens wherein the lenticules are aspherical in shape, with each lenticule divided into a plurality of coaxial zones and each zone having a different radius of curvature as disclosed in U.S. Pat. No. 4,545,007. Another attempted solution to the problem of non-uniform light distribution is disclosed in U.S. Pat. No. 5,043,856 as a mixture of spherical and aspherical lenticules uniformly distributed across the light-receiving surface of the lens. Random patterns such as shot stipple have also been tried.